Small signal threshold and proportional gain distributed digital communications

ABSTRACT

A method for signal gain adjustment in a multi-port, digital distributed antenna system uses a sorter to sort received signals in ascending order according to their signal levels. A threshold comparator generates a dynamic range fair threshold that is updated as any remaining system dynamic range is distributed amongst the remaining signals. Any received signal that is less than or equal to the threshold is attenuated with a unity gain factor. A signal that is greater than the threshold is attenuated with a gain factor that is inversely proportional to the signal level.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related to, and claims the benefit of thefiling date of, U.S. Provisional Patent Application No. 60/430,435,filed on Dec. 3, 2002.

TECHNICAL FIELD

The present invention relates generally to communications andparticularly to gain control of signals in a distributed antenna system.

BACKGROUND

Various types of wireless communication systems have become prevalentaround the world. For example, cellular communication systems cover mostmajor metropolitan areas as well as major highways through remote areas.Cellular systems permit individuals with cellular handsets tocommunicate with base stations that are connected to the public switchedtelephone network (PSTN) or some other communication network.

As with any communication system, cellular systems can leave coverage“holes” where the signal from the base stations cannot reach. The holescan be in tunnels, valleys, city streets between tall buildings, or anyother location where a radio frequency (RF) signal is blocked.

Placing additional base stations where these coverage holes are locatedis not always an option. Base stations tend to be very expensive due notonly to the cost of the equipment but also because of land acquisitioncosts. Additionally, large base station antennas may not fit within anarea either physically or aesthetically.

One solution to hole coverage is to use smaller distributed antennaswhere coverage is needed but a base station is not warranted or desired.There are problems, however, with using a distributed antenna system.

Any system has a certain dynamic range over which signals are processed.For a system that has only one antenna port, the entire dynamic range isavailable to the single port signal. When the system has multipleantenna ports, as in the distributed antenna system, the same dynamicrange is shared amongst the aggregate signal from all the ports. Thisreduces the dynamic range available for each port when multiple portsare simultaneously active. One problem with distributed antennas on asingle signal path is that the aggregate signal along the signal pathmay exceed the system's allowable dynamic range. There is a resultingneed in the art for adequately controlling the aggregate signal in asingle path distributed antenna system.

SUMMARY

The embodiments of the present invention encompass a method forproportional gain distribution in a system comprising a plurality ofdistributed antennas. A sampling function senses a signal level at eachof the plurality of distributed antennas. Each of the plurality ofsignal levels are compared with a dynamic range fair share threshold.Each signal level that is greater than the dynamic range fair sharethreshold is attenuated with a gain factor that is determined inresponse to a remaining portion of the total system dynamic range afterattenuation of other signal levels. Each signal level that is less thanor equal to the dynamic range fair share threshold are attenuated with aunity gain factor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of one embodiment of a distributed digitalantenna system of the present invention.

FIG. 2 shows a block diagram of another embodiment of a distributeddigital antenna system of the present invention.

FIG. 3 shows a block diagram of one embodiment of a remote unit inaccordance with the system of FIG. 1.

FIG. 4 shows a block diagram of one embodiment of a remote unit inaccordance with the system of FIG. 2.

FIG. 5 shows a block diagram of one embodiment of a system havingdistributed summation and gain control with head end common attenuation.

FIG. 6 shows a block diagram of one embodiment of a system havingdistributed summation and gain control with localized commonattenuation.

FIG. 7 shows a block diagram of one embodiment of a system havingdistributed summation and gain control with localized input attenuation.

FIG. 8 shows a block diagram of one embodiment of a system havingdistributed summation and gain control with head end common attenuation.

FIG. 9 shows a block diagram of one embodiment of a system havingdistributed summation and gain control with head end common attenuation.

FIG. 10 shows a block diagram of one embodiment of a method for fair andbalanced gain control in a distributed summation and gain control systemof the present invention.

FIG. 11 shows a flowchart of one embodiment of the fair-and balancedattenuation method of the present invention.

DETAILED DESCRIPTION

By distributing signal attenuation and control of the attenuation, theembodiments of the present invention retain the original system dynamicrange. A signal level threshold prevents small but valid signals frombeing attenuated to the point of being useless while the unused dynamicrange is redistributed to signals that require the additional dynamicrange.

The embodiments of the present invention refer to fiber optics as acommunications medium between remote units and the host unit. However,the communications medium connecting the remote units to the host unitcan take any form including a laser through an air interface, an RFsignal over coaxial cable, or an RF signal through an air interface.

FIG. 1 illustrates a block diagram of one embodiment of a distributeddigital antenna system of the present invention. The system has a basestation (100) that communicates over an RF link using an antenna (110).The base station communicates over the RF link using any appropriate airinterface standard. For example, the air interface standard comprisesone of Advanced Mobile Phone System (AMPS), code division multipleaccess (CDMA), time division multiple access (TDMA), Global System forMobile communications (GSM), or any other appropriate air interfacestandard.

The RF link is made up of a forward link over which the base station(100) transmits to a subscriber unit (150). The subscriber unit (150)transmits back to the base station (100) over a reverse link. Thesubscriber unit (150) is either a mobile station or a fixed station suchas in a wireless local loop system.

The base station (100) has the transmitters and receivers that enablethe subscriber unit (150) to communicate with the public switchedtelephone network (PSTN)(130). In one embodiment, the base station linksthe subscriber unit (150) to other subscriber units that arecommunicating with other base stations. In one embodiment, the basestation (100) is connected to the PSTN through a mobile switching centerthat handles the switching of calls with multiple base stations.

A host unit (101) is connected to the base station (100) through an RFlink (115). In one embodiment, this link (115) is a coaxial cable. Otherembodiments use other types of connections such as an air interface oran optical fiber carrying digital RF signals. U.S. patent applicationSer. No. 09/619,431, assigned to ADC Telecommunications, Inc. andincorporated herein by reference, discloses digital RF signals.

The host unit (101) is responsible for converting the RF signal from thebase station (100) to an optical signal for transmission over an opticalmedium. The host unit (101) also converts a received optical signal toan RF signal for transmission to the base station (100). In otherembodiments, the host unit (101) performs additional functions.

One or more remote units (105–108) are connected to the host unit (101)through an optical medium, such as fiber optic lines (120 and 125), in adaisy-chain arrangement. The remote units (105–108) are placed inlocations that require additional signal coverage due to a lack ofcoverage by the base station (100). The remote units (105–108)communicate with subscriber units in a particular remote unit's coveragearea over an RF link provided by the remote unit antennas (135–138).

For purposes of illustration, four remote units (105–108) are shown.However, alternate embodiments use other quantities of remote units. Ifonly a small geographic area requires coverage, as few as one remoteunit (105) is used. If a highway in a remote area requires additionalcoverage, more than four remote units are typically used.

The embodiment of FIG. 1 uses a separate fiber optic line for eachdirection of communication. Each fiber carries a different wavelength.For example, the fiber optic line (120) from the host unit (101) to theremote units (105–108) carries a wavelength of λ₁. The fiber optic line(125) from the remote units (105–108) to the host unit (101) carries awavelength of λ₂. In alternate embodiments, each fiber carries the samewavelength.

The fiber optic line (120) from the host unit (101) to the remote units(105–108) carries the digital optical signal for transmission by theremote units (105–108). The fiber optic line (125) from the remote units(105–108) carries a digital optical signal comprising the sum of thereceived signals from each of the remote units (105–108). The generationof this summation signal from the remote units is discussedsubsequently.

FIG. 2 illustrates a block diagram of another embodiment of adistributed digital antenna system of the present invention. This systemis similar to the embodiment of FIG. 1 except that the remote units(205–208) are connected to the host unit (201) over a single opticalmedium (220).

The system of FIG. 2 has a base station (200) that communicates over anRF link using an antenna (210). The base station can communicate overthe RF link using any air interface standard. For example, the airinterface standard may be code division multiple access (CDMA), timedivision multiple access (TDMA), or Global System for Mobilecommunications (GSM).

The RF link is made up of a forward link over which the base station(200) transmits to a subscriber unit (250). The subscriber unit (250)transmits back to the base station (200) over a reverse link. Thesubscriber unit (250) may be a mobile station or a fixed station such asin a wireless local loop system.

The base station (200) has the transmitters and receivers that enablethe subscriber unit (250) to communicate with the public switchedtelephone network (PSTN)(230). The base station may also link thesubscriber unit (250) to other subscriber units that are communicatingwith other base stations. In one embodiment, the base station (200) isconnected to the PSTN through a mobile switching center that handles theswitching of calls with multiple base stations.

A host unit (201) is connected to the base station (200) through an RFlink (215). In one embodiment, this link (215) is a coaxial cable. Otherembodiments use other types of connections such as an air interface oran optical fiber carrying digital RF signals.

The host unit (201) is responsible for converting the RF signal from thebase station (200) to a digital optical signal for transmission over anoptical medium. The host unit (201) also converts a received opticalsignal to an RF signal for transmission to the base station (200). Inother embodiments, the host unit (201) performs additional functions.

One or more remote units (205–208) are connected to the host unit (201)through an optical medium, such as a fiber optic line (220), that isconnected in a daisy-chain arrangement. The remote units (205–208) areplaced in locations that require additional signal coverage due to alack of coverage by the base station (200).

For purposes of illustration, four remote units (205–208) are shown.However, alternate embodiments use other quantities of remote unitsdepending on the application.

The embodiment of FIG. 2 uses a single fiber optic line (220) forcommunication both to and from the remote units (205–208). This isaccomplished by the single fiber (220) carrying multiple wavelengths.For example, the fiber optic line (220) uses a wavelength of λ₁, for thedigital signal from the host unit to the remote units (205–208). Thefiber optic line (220) also carries a digital summation signal with awavelength of λ₂. This digital summation signal is the sum of thereceived signals from the remote units (205–208). The generation of thissummation signal from the remote units is discussed subsequently.

FIG. 3 illustrates a block diagram of one embodiment of a remote unit(105) of FIG. 1. Each of the remote units (105–108) of the embodiment ofFIG. 1 are substantially identical in functional composition.

The remote unit (105) transmits and receives RF communication signalsover the antenna (135). Both the receive and transmit circuitry isconnected to the antenna (135) through a diplexer (301). Alternateembodiments use other quantities of antennas. For example, oneembodiment uses three antennas to cover three different sectors of anarea. In other embodiments, diversity antennas are used.

An analog signal that is received on the antenna (135) is split off bythe diplexer (301) to an analog-to-digital converter (305). Theanalog-to-digital converter (305) digitizes the received analog signalby periodically sampling the signal. The sampling generates a digitalrepresentation of the received analog signal. In one embodiment, thedigital signal comprises 14 bit samples of the received analog signal.

The digitized received signal is input to a summer (315) to be added tothe digitized signals from the preceding remote units in thedaisy-chain. The input of the summer (315), therefore, is coupled to anoutput of a previous remote unit. The output of the summer (315) is asummation signal that is coupled to either the input of a subsequentremote unit or to the host unit. The host unit thus receives a summationsignal that represents the sum of all the signals received by the remoteunits (105–108) of the system.

A digital signal from the host unit is coupled to a digital-to-analogconverter (310). The digital-to-analog converter (310) takes the digitalrepresentation of an analog signal and converts it to the analog signalfor transmission by the antenna (135).

Optical-to-Electrical converters (320–323) are located at the opticalports (330 and 335) of the remote unit (105). Each optical port (330 and335) has an input and an output that are each coupled to anOptical-to-Electrical converter (320–323).

Since the remote unit (105) operates with electrical signals that arerepresented by the optical signals coming in through the optical ports(330 and 335), the Optical-to-Electrical converters (320–323) areresponsible for converting the optical signals to electrical signals forprocessing by the remote unit (105). Received electrical signals areconverted from electrical to an optical representation for transmissionover the optical fiber.

FIG. 4 illustrates a block diagram of one embodiment of a remote unit(205) of FIG. 2. Each of the remote units (205–208) of the embodiment ofFIG. 1 is substantially identical in functional composition.

The remote unit (205) transmits and receives RF communication signalsover the antenna (435). Both the receive and transmit circuitry areconnected to the antenna (435) through a diplexer (401). Alternateembodiments use other quantities of antennas. For example, oneembodiment uses three antennas to cover three different sectors of anarea. In other embodiments, diversity antennas are used.

An analog signal that is received on the antenna (435) is split off bythe diplexer (401) to an analog-to-digital converter (405). Theanalog-to-digital converter (405) digitizes the received analog signalby periodically sampling the signal. The sampling generates a digitalrepresentation of the received analog signal. In one embodiment, thedigital signal comprises 14 bit samples of the received analog signal.

The digitized received signal is input to a summer (415) to be added tothe digitized signals from the preceding remote units in thedaisy-chain. The host unit thus receives a summation signal thatrepresents the sum of all the signals received by the remote units(205–208) of the system.

A digital signal from the host unit is coupled to a digital-to-analogconverter (410). The digital-to-analog converter (410) takes the digitalrepresentation of an analog signal and converts it to the analog signalfor transmission by the antenna (435).

Optical-to-Electrical converters (420–423) are located at the opticalports (440 and 445) of the remote unit (205). Each optical port (440 and445) has an input and an output that are each coupled to anOptical-to-Electrical converter (420–423).

Since the remote unit (205) operates with electrical signals that arerepresented by the optical signals coming in through the optical ports(440 and 445), the Optical-to-Electrical converters (420–423) areresponsible for converting the optical signals to electrical signals forprocessing by the remote unit (205). Received electrical signals areconverted from electrical to an optical representation for transmissionover the optical fiber.

A wavelength division multiplexer (WDM) (430 and 431) is located at eachoptical port (440 and 445). The WDMs (430 and 431) perform the opticalprocessing necessary to combine several optical signals having severalwavelengths. The WDMs (430 and 431) also perform the opticaldemultiplexing necessary to split the multiple wavelengths of a singlefiber to their own signal paths.

In the above-described embodiments, if one antenna port uses up all ofthe system's dynamic range, none is available for the other antennaports and the aggregate dynamic range needs to be increased. The amountof additional dynamic range required (in dB) is expressed as 20Log N,where N is the number of antenna ports. The quantity of additional bitsrequired in a frame in order to express the aggregate signal isexpressed as Log₂N.

As an example of one embodiment of operation, the dynamic range for 14bits is 84 dB. To accommodate the aggregate dynamic range for 32 antennaports, an additional 30 dB and 5 bits are required. In this case, theanalog-to-digital resolution for each port still remains at 14 bits butthe summation of all the antenna port signals is represented by 19 bits.

In order to keep the original dynamic range and output signal levels,the distributed attenuation of the embodiments of the present inventionuse attenuators at antenna port inputs, outputs, or both. Thedistributed control may use a head-end based controller with feedback toeach antenna port, local controllers at each antenna port, ordistributed control with distributed feedback.

The various embodiments of the present invention use automatic gainlimiting (AGL) as a gain control function. Alternate embodiments useautomatic gain control (AGC) as a gain control function. AGL is activeonly when the signal exceeds some maximum value. AGC continuouslycontrols attenuation.

The embodiments of the present invention employ different methods ofattenuation. These methods include stepped attenuation, continuousattenuation, and fair and balanced attenuation.

Stepped attenuation is used when the summation of all of the antennaports exceeds the maximum threshold. In one embodiment, this thresholdis unity. In this case, the attenuator provides attenuation in discreteincrements. For example, 6 dB increments can be accomplished in a binarynumber by bit shifting in the direction of a smaller value. One shiftequals 6 dB, two shifts equals 12 dB, and three shifts equals 18 dB.This can be continued for as much attenuation as required. For 32antenna ports, five shifts of 6 dB accommodates 30 dB of attenuation.

Continuous attenuation is continuous in value. The attenuation need notbe in fixed steps but the attenuation could be accomplished with exactlyas much as needed. In other words, the attenuation could be proportionalto the excess aggregate signal level. If the aggregate signal is 2.3 dBabove the maximum, the attenuator introduces exactly 2.3 dB ofattenuation.

This method of attenuation is accomplished by multiplying the aggregatevalue by the appropriate attenuation factor. In one embodiment, theattenuation factor is between 0, for infinite attenuation, and 1 for noattenuation.

Applying the attenuation to the aggregate signal means that all of thesignals are treated the same. The smallest signals suffer the most. Infact, very small signals may be attenuated to a level below the leastsignificant bit. At this point, such signals cease to exist.

A block diagram of the fair and balanced attenuation method isillustrated in FIG. 10. This method attenuates the smallest signals theleast and the largest signals are attenuated the most. Some of the verysmall signals may not receive any attenuation. An additional benefit isthat no portion of the dynamic range goes unused since it isprogressively allocated to the larger signals. In one embodiment, thefunctions of FIG. 10 are accomplished in the digital domain.

Referring to FIG. 10, in order to perform the fair and balancedattenuation method, each individual antenna port input is sensed with asampling function that is well known in the art to determine each inputsignal level. The signal levels are applied to the sorter (1001).

The sorter (1001) sorts the antenna port signals, designated x_(j), inascending order according to their level. In this case, j=1 is thesmallest and j=N is the largest, where N is the number of antenna ports.The sorted signals are input to a threshold comparator (1005) and a gaincalculator (1007). A “fair share” threshold is also input to thethreshold comparator. The dynamic range fair share threshold, K, iscalculated as K=T/(n−j) where the total available system dynamic rangeis unity and is designated as T. In alternate embodiments, otherappropriate threshold calculations are used.

The fair share threshold is dynamically redefined in order to divide anyremaining dynamic range among the remaining signals. The total remainingsystem dynamic range is calculated by a remaining dynamic rangecalculator (1009) that is also input to the threshold comparator (1005).The remaining dynamic range calculator (1009) uses the signal rangeinput from the gain calculator (1007) and the total dynamic range thatis assumed to be unity in this embodiment. The total remaining dynamicrange is expressed as T=T−y_(i) where y_(i) is the output signal fromthe antenna port. Alternate embodiments use other total dynamic ranges.

The gain calculator generates a gain, G_(j), from the thresholdcomparison results in order to progressively generate gain factors forPort 1-Port N in ascending order. The process of FIG. 10 can beexpressed as:

if x_(j) ≦ K, then Input signal, x_(j), is less than fair share do forj=1 to N G_(j) = 1 y_(j) = G_(j)*x T = T − y_(j) K = T/(N−j) end do elseRemaining input signals are more than fair share G_(j) = K/x_(j) Gain isinverse to signal level input y_(j) = G_(j)*x_(j) Reduce levelproportionally end if

The fair and balanced attenuation embodiment of FIG. 10 is illustratedin the following example using continuous attenuation:

Remaining Number of Fair Dynamic Remaining Index Input Share Gain OutputRange T Signals j x_(j) K G_(j) y_(j) 1 4 1 0.1 0.25 1 0.1 0.9 3 2 0.30.3 1 0.3 0.5 2 3 0.4 0.3 0.75 0.3 0.3 1 4 0.5 0.3 0.6 0.3 0 0

It can be seen in the table that the smallest signal (e.g., x_(j)=0.1)remains unchanged. It has been attenuated with a unity gain factor. Thenext smallest signal (e.g., x_(j)=0.3) takes advantage of the dynamicrange that is not used by the first signal. This signal is alsoattenuated with a unity gain factor.

The next largest signal (e.g., x_(j)=0.4) is attenuated by a gain factorof 0.75. The largest signal (e.g., x_(j)=0.5) is attenuated the most bya gain factor of 0.6.

The process of FIG. 10 can also be applied to a stepped attenuationembodiment. The following table illustrates such an embodiment. Itshould be noted that the 6 dB steps are for illustration purposes onlyand the present invention is not limited to any one attenuationincrement.

Remaining Number of Fair Dynamic Remaining Index Input Share Gain OutputRange T Signals j X_(j) K G_(j) Y_(j) 1 4 1 0.1 0.25 1 0.1 0.9 3 2 0.30.3 1 0.3 0.6 2 3 0.4 0.3 0.5 0.2 0.4 1 4 0.5 0.3 0.5 0.25 0.15 0

This table shows that the smallest signal remains unchanged since it isattenuated with a unity gain factor. The next smallest signal takesadvantage of the dynamic range not used by the first signal. This signalalso is attenuated with a unity gain factor.

The next largest signal is attenuated by a gain factor of 0.5. This is a6 dB step. Similarly, the largest signal is attenuated by a gain factorof 0.5. In this embodiment, a portion (e.g., 0.15) of the dynamic rangeis not used.

The following embodiments discuss certain transport path and aggregatesignal levels (e.g., 14 bits). This is for illustration purposes only.The present invention is not limited to any one transport path size oraggregate signal level.

FIG. 11 illustrates a flowchart of one embodiment of the fair andbalanced attenuation method of the present invention. The method beginswith determining if the input signal level is less than or equal to thethreshold, K (1101).

If they are not equal, the gain is determined to be the thresholddivided by the input signal level (1111). The output signal level isthen equal to the input signal level times the gain (1113).

If the input signal level is less than or equal to the threshold (1101),the gain is set equal to one (1103). The output signal level is thencomputed to be the input signal level times the gain (1105). Theremaining dynamic range is then reduced by the computed output signallevel (1107). The threshold is also recomputed as the remaining dynamicrange divided by the number of ports remaining (1109).

FIG. 5 illustrates a block diagram of one embodiment of a system havingdistributed summation with head end common attenuation and gain control.For purposes of clarity, a functional equivalent of the above-describedremote unit, in this and subsequent embodiments, is illustrated as anantenna (509) with a summation symbol (513).

The embodiment of FIG. 5 includes the four remote units (501–504) andthe host unit (505) as described previously. Each remote unit (501–504)has an antenna (506–509) that receives RF signals that are digitized andsummed (510–513) with any previous remote unit signals.

The summations (510–513) and transport path (530–532) to each remoteunit should have sufficient dynamic range to deliver the aggregatedynamic range. For example, in one embodiment the full dynamic range is19 bits for 32 antenna ports. This embodiment assumes that all of theremote units are substantially identical.

In the embodiment of FIG. 5, the host unit (505), located at the headend, performs the AGL (515) and attenuation (525) functions. The AGLsampling function (515) samples (520) the aggregate signal (534) fromthe last remote unit (504) before the host unit (505). This signalrequires 19 bits for a dynamic range of 114 dB. Other embodiments haveother bit quantities to represent different dynamic ranges.

If the AGL function (515) determines that the aggregate signal (531) isgreater than the maximum allowable dynamic range, the AGL function (515)instructs the attenuation function (525) to attenuate the signal. Theattenuation function (525) may use the stepped attenuation, thecontinuous attenuation, or other attenuation approaches.

In the example illustrated in FIG. 5 where the aggregate signal is 19bits, the attenuation function attenuates the signal to 14 bits. Thus,the signal from the host unit (505) to a base station will be within theallowable dynamic range.

FIG. 6 illustrates a block diagram of one embodiment of a system havingdistributed summation and gain control with localized commonattenuation. This embodiment uses a standard transport path (601–604)(e.g., 14 bits) by applying localized attenuation to its aggregatesignal.

Each remote unit (620–623) attenuates its common output level so thatthe maximum level is not exceeded. The aggregate of all summations(615–618) and attenuations (605–608) results in a head end aggregatesignal (630) that does not exceed the maximum level.

The AGL function (610–613) of each remote unit (620–623) samples thesignal level output (601–604) from the respective summation (615–618).If the signal level is greater than the allowable dynamic range, the AGLfunction (610–613) instructs its respective attenuation function(605–608) to attenuate that particular signal.

FIG. 7 illustrates a block diagram of one embodiment of a system havingdistributed summation and gain control with localized input attenuation.In this embodiment, each of the remote units (701–704) uses an AGLfunction (725–728) to control attenuation functions (710–713 and720–723) on the summation (730–733) inputs.

The input signals that are attenuated in this embodiment include boththe antenna port and the downstream port. For example, in one remoteunit (702) the AGL function (726) samples the downstream signal path(750) and the antenna port input (751). If the dynamic range of eitherinput is greater than the allowable maximum, the AGL function (726)instructs the attenuation function (711 and/or 721) of the appropriateinput to attenuate that particular signal.

The fair and balanced attenuation method can be employed in theembodiment of FIG. 7 as illustrated in FIGS. 10 and 11. However, thisembodiment is not limited to any one attenuation method.

FIG. 8 illustrates a block diagram of one embodiment of a system havingdistributed summation and gain control with head end controlled,distributed attenuation. This embodiment uses an AGL function (820) atthe host unit (825) to provide feedback (830) to the remote units(801–804).

Each remote unit (801–804) has an attenuation function (810–813) at theantenna port to provide appropriate attenuation to the input signal. AnAGL function (815–818) samples the antenna port's received signal inorder to provide individual attenuation instructions to the attenuationfunctions (810–813).

The embodiment of FIG. 8 additionally uses an AGL function (820) at thehost unit (825) to sample the final aggregate signal (831). The hostunit's AGL function (820) provides a head end feedback attenuationsignal (830) to the remote units' AGL functions (815–818) to use inconjunction with the sampled input communication signal levels. Thisfeedback signal (830) may take the form of one or more bits in the databeing transmitted along the optical medium to the remote units (801–804)from the host unit (825).

For the case of continuous attenuation, the feedback attenuation signalis an attenuation factor that is comprised of a value between 0 and 1.For example, an unattenuated aggregate of 2 would be represented by anattenuation factor of 0.5. The attenuation factor is not applieddirectly to the individual remote units' attenuation functions(810–813). Instead, if a port signal is more than 0.5 of the totaldynamic range, the remote units' AGL function (815–818) instructs theappropriate attenuation function (810–813) to apply a 0.5 attenuationfactor to the port input. If the signal is equal to or less than 0.5,attenuation is not applied.

Since some of the signals may not be attenuated, the resulting aggregatesignal may still be slightly too high. In this case, the AGL function(820) at the host unit (825) adjusts its feedback attenuation factor towhatever value is needed (e.g., 0.4). This value is dynamic and islowered until the desired aggregate signal level is achieved.

Using the continuous attenuation method, the host unit's AGL function(820) samples the final aggregate signal (831) from the remote unit(804) nearest the head end. If the level of the final aggregate signal(831) is too large, the host unit (825) provides a feedback attenuationfactor that starts at one and slews down toward zero. When the finalaggregate signal level is within bounds (i.e., less than the maximumdynamic range), the host unit holds this attenuation factor.

If the final aggregate signal level later decreases sufficiently, thehost unit (825) slowly raises the attenuation factor back toward one.All of the remote units (801–804) apply attenuation only to their ownports according to the fair and balanced attenuation method discussedpreviously. This means that the applied attenuation depends on therespective antenna port's input level as well as the feedback factor(830).

Using the stepped attenuation method, the host unit (825) samples thefinal aggregate signal (831) from the remote unit (804) nearest the headend. If the final aggregate signal (831) is too large, the host unit(825) provides a feedback attenuation signal that is an attenuationnumber that starts at 0 and increments towards 6. This is assuming 6 dBsteps. Other embodiments use other increments.

When the final aggregate signal level is less than or equal to 0 dB(unity gain), the host unit's AGL function (820) holds this number. Ifthe final aggregate signal level decreases to a predetermined level(e.g., −12 dB), the host unit decrements the number back towards 0. Thedecrementing occurs after a delay due to system end-to-end response.

In one embodiment, all of the remote units (801–804) apply attenuationto their own ports according to the fair and balanced attenuation methoddiscussed previously. This means that the applied attenuation depends onthe respective antenna port's input level as well as the feedbacknumber.

The following table illustrates one example of the stepped fairattenuation as applied to the embodiment of FIG. 8:

Actual Applied Attenuation Port Signal Level Step MaxPossible >−6 >−12 >−18 >−24 >−30 Number Attenuation dB dB dB dB dB 0  0dB 0 0 0 0 0 1  6 dB −6 0 0 0 0 2 12 dB −12 −6 0 0 0 3 18 dB −18 −12 −60 0 4 24 dB −24 −18 −12 −6 0 5 30 dB −30 −24 −18 −12 −6

It can be seen in the table that a remote unit's attenuation onlyaffects its port signals. There is a 12 dB window between the decisionto increase attenuation and the decision to decrease attenuation. If allports have the same signal level, a step increment affects them all andcauses 6 dB more attenuation in both the individual and aggregate signallevels. But if some of the signals are of different levels, only thelargest signals are attenuated by 6 dB. This results in an aggregateadditional level attenuation that is less than 6 dB.

FIG. 9 illustrates a block diagram of one embodiment of a system havingdistributed summation and gain control. This embodiment puts theattenuation decision making with the individual remote units (901–904)while still providing the feedback of the attenuation factor.

In this embodiment, the final aggregate signal is sampled and a feedbackattenuation factor is passed toward the tail end of the system. Thefeedback can be accomplished by embedding the attenuation factor in adata frame that is transmitted over the communication medium to theremote units. The data frame format and use is well known in the art andnot discussed further. In other embodiments, dedicated bits or acontinuous value are used for the feedback.

Similarly, the AGL function (910–913) of each remote unit (901–904) alsosamples the aggregate signal at the output of the summation (920–923)for that particular unit. The sampling AGL function then passes anattenuation factor to the preceding remote unit's AGL function (910–913)in a data frame.

As an example, the AGL function (913) of the head end remote unit (904)samples the final aggregate signal level and generates an attenuationfactor. This factor is fed back in the direction of the tail end to thenext remote unit (903) in the daisy-chain. This remote unit (903)samples the signal level out of the summation (922) at that unit andgenerates an attenuation factor based on that level. This factor is fedback to the next remote unit (902) in the daisy-chain.

Every remote units' (901–904) AGL function (910–913) has two attenuationfactors: the one from its local evaluation of its antenna port (i.e.,the local attenuation signal) and the one from the upstream unit (i.e.,towards the head end). The AGL function (910–913) applies the moresevere factor of the two to its port attenuation and passes this factoron toward the tail end.

In this embodiment, the host unit generates the highest attenuationfactor because its aggregate signal is the largest. Because of thefeedback, all remote units use this factor to apply attenuation. Sinceall of the remote units also sample their own antenna port, they willapply no attenuation or little attenuation to sufficiently smallsignals. The remote units will also apply large attenuation to largesignals.

If there is a break in the feedback path, the aggregate sampling at eachremote unit prevents any unit's aggregate signal from overflowing.Furthermore, all units from the tail end to the point of the break willperform fair sharing of the aggregate signals amongst themselves.Similarly, all units from the break to the head end will perform fairsharing of the aggregate signals amongst themselves. However, the tailend group is favored over the head end group.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

1. A method for gain distribution in a system comprising a plurality ofdistributed antennas and a total system dynamic range, the methodcomprising: sensing a signal level at each of the plurality ofdistributed antennas; comparing at least one of the plurality of signallevels with a dynamic range fair share threshold; and attenuating eachof the at least one of the compared signal levels that is greater thanthe dynamic range fair share threshold with a gain factor that isdetermined in response to a remaining portion of the total systemdynamic range after attenuation of other signal levels of the pluralityof signal levels.
 2. The method of claim 1 wherein the dynamic rangefair share threshold is initially determined by an inverse of a quantityof the plurality of distributed antennas.
 3. The method of claim 1 andfurther including: sorting the sensed signal levels in an ascendingorder prior to comparing; and updating the total system dynamic range,after attenuation of each signal level, by allocating unused totalsystem dynamic range to subsequently attenuated signal levels.
 4. Themethod of claim 1 and further including attenuating with unity gainsignal levels that are less, than or equal to the dynamic range fairshare threshold.
 5. The method of claim 1 wherein if the signal level isgreater than the dynamic range fair share threshold, the gain factorapplied to a first signal level is inversely proportional to the firstsignal level.
 6. The method of claim 5 wherein the gain factor issubstantially equal to K/x_(j) where K is an inverse of a quantity ofthe plurality of distributed antennas and x_(j) is the first signallevel.
 7. A method for gain distribution in a distributed antenna systemhaving a total dynamic range, the method comprising: sorting a pluralityof signal levels from the distributed antenna system; comparing each ofthe sorted signal levels with a dynamic range fair share threshold; if afirst signal level is less than or equal to the dynamic range fair sharethreshold, applying a unity gain factor to the first signal level anddividing remaining total dynamic range between remaining signal levelsof the plurality of signal levels; and if the first signal level isgreater than the dynamic range fair share threshold, applying a gainfactor that is inversely proportional to the first signal level.
 8. Themethod of claim 7 wherein the gain factor that is substantially equal tothe inverse of the first signal level is equal to a quantity ofdistributed antennas in the distributed antenna system divided by thefirst signal level.
 9. The method of claim 7 wherein the plurality ofsignal levels are sorted in ascending order.
 10. A method for gaindistribution in a distributed antenna system having a system dynamicrange, the method comprising: sorting, in ascending order, a pluralityof signal levels from the distributed antenna system; comparing a firstsignal level of the plurality of sorted signal levels with a dynamicrange fair share threshold; if the first signal level is less than orequal to the dynamic range fair share threshold, applying a unity gainfactor to the first signal level; if the unity gain factor has beenapplied to the first signal level, updating the dynamic range fair sharethreshold to allocate remaining system dynamic range between remainingsignal levels; and if the first signal level is greater than the dynamicrange fair share threshold, applying a first gain factor that issubstantially equal to the dynamic range fair share threshold divided bythe first signal level.
 11. The method of claim 10 and further includingapplying a second gain factor to a second signal level if the secondsignal level is greater than the dynamic range fair share threshold, thesecond gain factor being substantially equal to the dynamic range fairshare threshold divided by the second signal level.
 12. The method ofclaim 10 and further including if the unity gain factor has been appliedto the first signal level, updating the system dynamic range bydecreasing the remaining system dynamic range by the first signal levelto which the gain factor has been applied.
 13. A method for gaindistribution in a distributed antenna system having a system dynamicrange, the method comprising: sensing a signal level for each of aplurality of received signals from the distributed antenna system;sorting, in ascending order, the plurality of signal levels; comparing afirst signal level of the plurality of sorted signal levels with adynamic range fair share threshold; if the first signal level is lessthan or equal to the dynamic range fair share threshold, applying aunity gain factor to the first signal level; if the unity gain factorhas been applied to the first signal level, updating the dynamic rangefair share threshold to allocate remaining system dynamic range betweenremaining signal levels; and if the first signal level is greater thanthe dynamic range fair share threshold, applying a first gain factorthat is substantially equal to the dynamic range fair share thresholddivided by the first signal level.
 14. A distributed antenna systemhaving gain distribution and a total dynamic range, the systemcomprising: a plurality of distributed antennas that receive signalseach having a signal level; a sorter that sorts the received signalsaccording to each signal level; threshold comparator coupled to thesorter, that generates comparison results in response to a comparisonbetween a sorted signal and a dynamic range fair share threshold that isupdated with a remaining system dynamic range; a remaining dynamic rangecalculator that generates the remaining system dynamic range bydecreasing the total dynamic range by each attenuated signal level; anda gain calculator, coupled to the sorter, the threshold comparator, andthe remaining dynamic range calculator, that progressively generatesgain factors in response to the comparison results.
 15. The distributedantenna system of claim 14 wherein the distributed antennas are coupledthrough distributed summers over a communication medium.
 16. Thedistributed antenna system of claim 15 wherein the communication mediumis an optical medium.
 17. The distributed antenna system of claim 14wherein the sorter sorts the received signals in ascending order inresponse to each'signal level.
 18. A distributed antenna system havinggain distribution and a total dynamic range, the system comprising: aplurality of distributed antennas that receive signals each having asignal level; a signal level sampling function that senses each signallevel; a sorter that sorts the received signals in ascending orderaccording to each signal level; a threshold comparator, coupled to thesorter, that generates a comparison result in response to a comparisonbetween a sorted signal and a dynamic range fair share threshold that isupdated with a remaining system dynamic range; a remaining dynamic rangecalculator that generates the remaining system dynamic range bydecreasing the total dynamic range by each attenuated signal level; again calculator, coupled to the sorter, the threshold comparator, andthe remaining dynamic range calculator, that progressively generates again factor for each received signal in ascending order in response toeach comparison result; and a plurality of attenuators, each attenuatorcoupled to a received signal, for attenuating each received signal inresponse-to its gain factor.
 19. The system of claim 18 wherein the gaincalculator generates a gain factor of unity for a received signal if itssignal level is less than or equal to the dynamic range fair sharethreshold.
 20. The system of claim 18 wherein the gain factors aregenerated in discrete increments.
 21. A distributed antenna systemhaving gain distribution and a total dynamic range, the systemcomprising: a plurality of distributed antennas that receive analogsignals each having a signal level represented in a digital form; ananalog to digital converter that converts the analog signals to digitalsignals; a sorter that sorts the digital signals according to eachsignal level; a threshold comparator, coupled to the sorter, thatgenerates a comparison result in response to a comparison between asorted signal and a dynamic range fair share threshold that is updatedwith a remaining system dynamic range; a remaining dynamic rangecalculator that generates the remaining system dynamic range bydecreasing the total dynamic range by each attenuated signal level; anda gain calculator, coupled to the sorter, the threshold comparator, andthe remaining dynamic range calculator, that progressively generatesgain factors in response to the comparison results.
 22. A method forgain distribution in a distributed antenna system having a systemdynamic range, the distributed antenna system being coupled by anoptical network, the method comprising: receiving a plurality of analogsignals; converting each analog signal to a digital signal having asignal level expressed in a digital format; sorting, in ascending order,the plurality of digital signals according to their signal levels;comparing a first digital signal level of the plurality of digitalsignals with a dynamic range fair share threshold; if the first digitalsignal level is less than or equal to the dynamic range fair sharethreshold, applying a unity gain factor to the first digital signallevel; if the unity gain factor has been applied to the first digitalsignal level, updating the dynamic range fair share threshold toallocate remaining system dynamic range between remaining digitalsignals; and if the first digital signal level is greater than thedynamic range fair share threshold, applying a first gain factor that issubstantially equal to the dynamic range fair share threshold divided bythe first digital signal level.